Plants in the flowering stage need to ensure reproduction by protecting themselves from attack and by preserving interactions with mutualist pollinators. When different plant mutualists are using the same type of cues, such as volatile compounds, attraction of parasitoids and pollinators may trade off. To explore this, we compared volatile emission of Brassica nigra plants in response to single or dual attack on their inflorescences. Additionally, we recorded flower visitation by pollinators and the attraction of parasitoids in the greenhouse and/or field. Brassica nigra were exposed in the flowering stage to one or two of the following three attackers: Brevicoryne brassicae aphids, Pieris brassicae caterpillars, and Xanthomonas campestris pv. raphani bacteria. We found that single attack by caterpillars, and dual attack by caterpillars plus aphids, induced the strongest changes in plant volatile emission. The caterpillars' parasitoid C. glomerata did not exhibit preference for plants exposed to caterpillars only vs. plants exposed to caterpillars plus aphids or plus bacteria. However, the composition of the pollinator community associated with flowers of B. nigra was affected by plant exposure to the attackers, but the total number of pollinators visiting the plants did not change upon attack. We conclude that, when B. nigra were exposed to single or dual attack on their inflorescences, the plants maintained interactions with natural enemies of the insect attackers and with pollinators. We discuss how chemical diversity may contribute to plant resilience upon attack.
Keywords: Brassica nigra (Brassicaceae); Flowering plants; Indirect resistance; Multiple attack; Plant volatiles; Pollination.